I'm doing some research on creating a SIP server that will work with Google Voice. My goal is set up a service so when I'm within a Wifi network, it will default to the SIP phone. When I'm not within a Wifi network, it will fall back to the service provider. The point of this project is to save some money by switching to a pay-as-you-use contract. I'm almost always within a Wifi network, so this should work out.

It looks like Yate is able to handle Google Voice (I heard Asterisk is flaky with Google Voice). Now I need a SIP phone to go with it.